[Docs] Update api-constructor.md

[PedroPovedaQ]

Add closing parenthesis so code example runs correctly (compiler error)

[coveralls]

Coverage remained the same at 100.0% when pulling 4b62289 on PedroPovedaQ:patch-1 into 0dc325d on lovell:master.

[lovell]

Hello, thanks for the PR to fix this.

Did you see the Update this documentation by updating the source code message at the top of the file?

Please can you update the JSDocs here:

sharp/lib/constructor.js

Line 120 in 0dc325d

* }.toFile('noise.png');

...then run npm run docs-build to rebuild the markdown file.

[lovell]

Landed as 2020839 - thank you!